1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for routing ported out calls, and specifically to performing Local Number Portability (LNP) queries by Signal Transfer Points (STPs).
2. Backaround and Objects of the Present Invention
Since the beginning of the telephone in the 1870's, signaling has been an integral part of telephone communications. The first telephone devices depended on the receiving party standing next to the receiver at the time of the call. Later, after the formation of the Bell Telephone Company, Alexander Graham Bell's assistant Watson invented the telephone ringer, eliminating the foreknowledge requirement. By lifting the receiver and allowing DC current to flow through the phone and back through the return of the circuit, a lamp would be lit on the exchange operator's switchboard to signal the operator that a call was trying to be placed.
However, early signaling methods were somewhat limited because they used the same circuit for both signaling and voice. In addition, they were analog and had a limited number of states, or values, that could be represented. In the early 1960's, Europe began digitizing the network, removing the signaling from the voice network, and placing the phone signals on a separate network. With this division of signaling and voice, the call setup and tear-down procedures required with every phone call were performed faster, while reserving the separate voice and data circuits for use when a connection was possible, e.g., no voice connection is needed when the called party's number is busy. Common Channel Signaling (CCS), which uses a digital facility, but places the signaling information in a time slot or channel separate from that of the voice or data it is related to, has become the foundation for telecommunications today.
In modern telecommunications networks, signaling constitutes the distinct control infrastructure that enables provision of all other services. It can be defined as the system that enables stored program control exchanges, network databases, and other "intelligent" nodes of the network to exchange: (a) messages related to call setup, supervision, and tear-down; (b) information needed for distributed applications processing (inter-process query/response); and (c) network management information.
In addition, the Intelligent Network (IN) and the new Advanced Intelligent Network (AIN) have made possible the transfer of all types of information through the telephone network without special circuits or long installation cycles. In the IN, everything is controlled or configured by workstations with user-friendly software. Telephone service representatives can, therefore, create new services and tailor a subscriber's service from a terminal while talking with the customer. These changes are immediately and inexpensively implemented in the switches, rather than by the more traditional method: expensive programming changes made by certified technicians.
The IN consists of a series of intelligent nodes, each capable of processing at various levels, and each capable of communicating with one another over data links. The basic infrastructure needed is composed of various signaling points, which both perform message discrimination (read the address and determine if the message is for that node), and route messages to other signaling points. The basic three types of signaling points are: (1) Service Switching Points (SSPs); (2) Signal Transfer Points (STPs); and (3) Service Control Points (SCPs), each of which are described in more detail hereinafter.
With reference now to FIG. 1 of the drawings, the many Service Switching Points (SSPs) 100 serve as the local exchanges in a telephone network 90, a portion of which is shown in FIG. 1. The SSPs 100 also provide an Integrated Services Digital Network (ISDN) interface for the Signal Transfer Points (STPs) 110, as is understood in the art. The ISDN is the subscriber interface to the IN.
The STP 110 serves as a router, and switches messages received from a particular SSP 100 through the network 90 to their appropriate destinations (another SSP 100). As is also understood in the art, the STP 110 receives messages in packet form from the SSPs 100. These packets are either related to call connections or database queries. If the packet is a request to connect a call, the message must be forwarded to a destination end office (another SSP 100), where the call will be terminated.
If, however, the message is a database query seeking additional information, the destination will be a database. Database access is provided through the Service Control Point (SCP) 120, which does not store the information, but acts as an interface to a computer that houses the requested information.
Presently, a subscriber on one SSP 100 has the ability to move to a different SSP 100 while retaining their public directory number. This is referred to as number portability. One key advantage of number portability is that other subscribers can connect to the portable subscriber without any changes to their dialing procedures.
If a subscriber has been ported out to another SSP 100, the Initial Address Message (IAM) sent by the originating SSP 100 must be modified to account for the change in the terminating SSP. The Local Number Portability (LNP) is the database that holds the Location Routing Number (LRN), which is a ten-digit number used to uniquely identify the switch that has the ported-out number. Specifically, the LRN is the number for the recipient switch, which is the switch that has ported in a number from another switch (called a donor switch). This ported-in number was not previously served by the recipient switch.
Typically, the SSP 100 sends a LNP query to the SCP 120, which accesses the LNP database in order to retrieve the routing information for a ported subscriber. The query response by the SCP 120 provides that SSP 100 with both the pertinent LRN, which is populated (that is placed) in the Called Party Number (CPN) parameter in the IAM, and the Ported Dialed Number (PDN), e.g., the actual dialed digits for the ported-out subscriber, which is placed in the Generic Address Parameter (GAP) in the IAM. The Forward Call Indicator (FCI) (M-bit) in the IAM is then updated to indicate that the number has been translated. The FCI M-bit is used as a fail-safe mechanism to prevent more than one LNP query from being launched on a call.
However, with non-AIN capable SSP's, the SSP's are unable to initiate the LRN query or receive LRN information from the SCP 120. Therefore, non-AIN capable SSPs have to be able to identify whether an incoming call terminates to its own switch from the Called Party Number (CPN) without the aid of the LRN. After a call is determined to not terminate on its own switch, the local SSP 100 routes the call according to its existing number analysis database. This involves routing the call to the aforementioned donor switch or a tandem (intermediate) switch that has LNP access capability. The donor or tandem switch then launches the query to determine routing, a process which results in excessive switching and delays.
However, if the first six digits of the CPN point back to the SSPs route (indicating that a number has been ported out), the call is typically transmitted to an affiliated exchange, over a dedicated route, by bilateral agreement, to handle routing for ported out subscribers from the non-AIN capable SSP 100. This process is also expensive and time-consuming, as is understood in the art.
It is therefore one object of the invention to allow non-AIN capable SSPs access to the LNP database without expensive upgrading.
It is a further object of the invention to reduce the switching processes and the cost associated with LNP queries by AIN-capable SSPs.